Backfire and Flashback
In oxy-fuel welding and cutting, if the system is not properly purged of air and all connections are not tight before lighting the torch, the flame may burn inside the torch instead of at the tip. This can result in either a backfire or a flashback.
Backfire
A backfire is a momentary burning of the flame back into the torch tip.
Oxy-Fuel Torch Backfire
A backfire is usually characterized by a loud snap or pop as the flame goes out. Since it is normally less serious, you can typically relight the torch without difficulty. However, if backfiring continues each time the torch is lit, check for these possible causes:
- Overheated tip
- Gas working pressures greater recommended for the tip size being used
- Loose tip
- Dirt on the torch tip seat
Flashback
A flashback occurs when the flame burns inside or beyond the torch mixing chamber. It is more dangerous than a backfire.
Flashback Safety
A flashback is usually accompanied by a hissing or squealing sound, and the flame at the tip becomes smoky and sharply pointed. Flashbacks can result from the same causes as backfires, but may also indicate:
- Improper handling
- Damaged or cracked torch head
- Distorted components in the torch
You can stop the flashback at once if you close the oxygen valve immediately.
In most instances, backfires and flashbacks result from carelessness. You can avoid these difficulties by making certain that:
- All connections in the system are clean and tight
- Torch valves are closed (not open or merely loosely closed) when the equipment is stowed
- The oxygen and acetylene working pressures used are those recommended for the torch employed
- The system is purged of air before the apparatus is used
Flashback Safety: If a flashback occurs, immediately close the oxygen valve first, then the acetylene valve. This action will stop the flashback quickly.
Prevention of Backfires and Flashbacks:
Most backfires and flashbacks result from carelessness. You can help prevent them by ensuring:- All system connections are clean and tight
- Torch valves are fully closed when not in use
- Correct oxygen and acetylene pressures are used for the torch and tip size
- The system is properly purged of air before use
Purging is especially important when new hoses, torches, or gas cylinders are connected to the system.
Knowledge Check Choose the best answer for the question.
2-10. A welder hears a loud pop and the flame goes out while lighting the torch. What has most likely occurred?
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